1. Field of the Invention
The present invention relates to a liquid crystal display device and, in particular, a technology effectively applied to lateral electric field drive type liquid crystal display devices.
2. Description of the Related Art
In liquid crystal display devices that are mounted to cell phones, digital cameras, and the like, in recent years, resolution is increasing (the number of pixels is increasing) progressively and the areal dimensions per pixel tend to decrease accordingly. Further, the demand for high image quality is still strong in those liquid crystal display devices. Therefore, those liquid crystal display devices are required to balance high image quality and high pixel count. Major factors that give a liquid crystal display device high image quality are brightness, contrast ratio, and viewing angle characteristics.
An in-plane switching (IPS) liquid crystal display device includes a liquid crystal display panel including, in each pixel, an electrode that is characterized by being shaped in a stripe pattern in plan view, and drives a liquid crystal layer by applying an electric field whose major components are parallel to the substrate plane (so-called lateral electric field) to the liquid crystal layer. The liquid crystal layer in the IPS liquid crystal display panel has a homogeneous alignment, and an application of a lateral electric field causes an alignment change in which liquid crystal molecules rotate within the plane of the liquid crystal layer. The IPS liquid crystal display panel therefore has excellent display characteristics in terms of viewing angle.
When a lateral electric field is applied to the liquid crystal layer having a homogeneous alignment, there are two possible rotation directions, clockwise and counter-clockwise, for the liquid crystal molecules. Generally, when the liquid crystal molecules rotate, a rotation direction that requires a smaller rotation angle to be parallel to the electric field direction is chosen. Therefore, in the IPS liquid crystal display device, the liquid crystal molecules can be prompted to rotate in one of the two possible directions by setting the direction of the electrode stripes (electric field direction) and the initial alignment direction of the liquid crystal layer suitably.
In some recent IPS liquid crystal display panels, an area that exhibits a clockwise alignment change (hereinafter, referred to as clockwise area) and an area that exhibits a counter-clockwise alignment change (hereinafter, referred to as counter-clockwise area) are formed within a single pixel by, for example, setting two electrode stripe directions within a single pixel. A liquid crystal display device that includes this type of liquid crystal display panel is even more improved in tone reproduction in the viewing angle direction.
IPS liquid crystal display panels include ones called IPS provectus (IPS-Pro) liquid crystal display panels in which a pixel electrode and a common electrode are disposed in different layers, and one of the pixel electrode and the common electrode that is disposed closer to a liquid crystal layer than the other electrode is has a stripe-patterned shape in plan view, whereas the other electrode that is disposed farther from the liquid crystal layer than the one electrode is has a solid flat shape in plan view. IPS-Pro liquid crystal display devices have higher transmittance and are capable of brighter display compared to, for example, IPS liquid crystal display devices which dispose a pixel electrode and a common electrode in the same layer. Liquid crystal display panels capable of color display commonly use a pixel that has a substantially rectangular shape in plan view. In those liquid crystal display panels, setting the stripe direction of a stripe-patterned electrode parallel to the longer sides of the pixel lessens the transmittance-lowering effect of a domain that is generated at an end of the electrode, and accordingly enhances the transmittance.
In other words, IPS-Pro liquid crystal display devices can have excellent viewing angle characteristics and high transmittance both by employing a pixel structure (planar shape) in which the stripe direction of the stripe-patterned electrode is set parallel to the direction of the longer sides of the pixel, and the stripe direction has two variations. A well known example of this pixel structure is a structure in which the longer sides of the pixel are bent into a boomerang shape (see JP 2009-181092 A, for example).